Exhaust gas recirculation valve having a rotary motor

ABSTRACT

An exhaust gas recirculation valve is provided. The exhaust gas recirculation valve has a base, a spring biasing the valve closed, and an actuator including a rotary motor and a linearly displaceable shaft that is coupled to the motor&#39;s rotor. The valve includes a valve member and valve seat disposed within a fluid conduit, and the spring is disposed between the actuator and the valve.

PRIORITY

This application is a continuation application of U.S. application Ser.No. 10/759,230, filed Jan. 20, 2004, entitled “Exhaust Gas RecirculationValve Having a Rotary Motor,” by Gary Everingham and Kirk Ivens, whichis hereby incorporated by reference in its entirety, which claims thebenefit of U.S. Provisional Application Ser. No. 60/440,857 entitled“Synchronous Motor Exhaust Gas Recirculation Valve” by Gary Everinghamand Kirk Ivens and filed on Jan. 17, 2003, which provisional applicationis hereby incorporated by reference in its entirety. The parent U.S.application Ser. No. 10/759,230 is related to U.S. application Ser. No.10/759,229 (“Exhaust Gas Recirculation Valve Having a Rotary Motor”)filed on Jan. 20, 2004, and to U.S. application Ser. No. 10/759,231(“Exhaust Gas Recirculation Valve Having a Rotary Motor”) filed on Jan.20, 2004.

BACKGROUND OF THE INVENTION

Controlled engine exhaust gas recirculation (“EGR”) is a known techniquefor reducing oxides of nitrogen in products of combustion that areexhausted from an internal combustion engine to atmosphere. A known EGRsystem employs an EGR valve that is controlled in accordance with engineoperating conditions to regulate the amount of engine exhaust gas thatis recirculated to the induction fuel-air flow entering the engine forcombustion so as to limit the combustion temperature and hence reducethe formation of oxides of nitrogen.

It is known to mount an EGR valve on an engine manifold where the valveis subjected to a harsh operating environment that includes widetemperature extremes and vibrations. Stringent demands are imposed bygovernmental regulation of exhaust emissions that have created a needfor improved control of such valves. Use of an electric actuator is onemeans for obtaining improved control, but in order to be commerciallysuccessful, such an actuator must be able to operate properly in suchextreme environments for an extended period of usage. Moreover, inmass-production automotive vehicle applications, componentcost-effectiveness and size may be significant considerations.

A known EGR valve typically relies on a valve that is actuated by amovement of a valve stem by an electromagnetic actuator. The EGR valveis typically mounted to a manifold or a housing that has one portexposed to exhaust gases and another port exposed to an intake manifoldof the engine. Under certain operating conditions, the valve abuts avalve seat surface so as to prevent exhaust gases from flowing into theintake manifold. Depending on the operating conditions, the valve can bemoved away from the seat to permit a controlled amount of exhaust gasesinto the intake manifold.

An EGR valve having a linear actuator including a rotary motor, whichpossesses more accurate, quicker and generally linear responses can beadvantageous by providing improved control of tailpipe emissions,improved driveability, and/or improved fuel economy for a vehicle havingan internal combustion engine that is equipped with an EGR system.

Further, an EGR valve having a linear actuator including a rotary motor,which is more compact in size while delivering the same or an increasedmagnitude of force over the travel of the valve stroke can beadvantageous because of limitations on available space in a vehicleengine compartment. Thus, it would be advantageous to provide for an EGRvalve that is compact yet powerful enough to deliver a generallyconstant force over an extended stroke distance.

SUMMARY OF THE INVENTION

In one preferred embodiment, a method for assembling an exhaust gasrecirculation (EGR) valve is provided. This method includes providing abase having a fluid conduit extending between first and second ports, avalve member disposed within the fluid conduit, and a valve shaft havinga first end fixed to the valve member and a second end, and mounting alinear actuator with a rotary motor to the base, the actuator includinga displaceable member that is decoupled from the valve shaft.

In another embodiment, a method of operating an exhaust gasrecirculation valve is provided including the steps of providing a valveportion including a valve member engaged with a valve seat when thevalve portion is in a closed position, a valve stem having alongitudinal axis, a first end secured to the valve member and a secondend, and a spring that biases the valve member into engagement with thevalve seat. This method also includes the steps of providing a linearactuator including a rotary motor and a displaceable member coupled tothe motor's rotor, wherein the rotation axis of the rotor issubstantially parallel to the longitudinal axis, and opening the valveincluding pushing the displaceable member into the valve stem secondend.

In a method for closing an EGR valve, there includes the steps ofproviding a linear actuator having a rotary motor, providing a base, avalve member disposed within the base and being engaged with a valveseat when the valve is closed and the valve member being lineardisplaced from the valve seat when configured from the closed to an openposition, providing a spring disposed below the actuator wherein thespring is compressed when the valve is open and upon power loss to themotor, closing the valve including expanding the compressed spring.

BRIEF DESCRIPTIONS OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate embodiments of the invention,and, together with the general description given above and the detaileddescription given below, serve to explain the features of the invention.

FIG. 1 is a cross-sectional view of an EGR valve configured in an openposition.

FIG. 2 is a cross-sectional view of the EGR valve of FIG. 1 configuredin a closed position.

FIG. 3 illustrates a portion of an actuator of the EGR valve of FIGS. 1and 2 including a lead screw and a nut.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

FIGS. 1 and 2 illustrate cross-sectional views of an embodiment of anexhaust gas recirculation EGR valve 10 according to a preferredembodiment. EGR valve 10 includes a base 12, bracket 14 and a valveactuator 16. Actuator 16 includes any suitable rotary motor (e.g.,stepper, synchronous, DC) and a shaft 60 coupled to the motor's rotor.Preferably, a DC motor is used, and more preferably, a brushless DCmotor is used. Actuator 16 may be used to configure valve 10 among aplurality of open positions and a closed position on command from anengine control unit (ECU). FIG. 2 illustrates a closed position and FIG.1 illustrates one such open position. Shaft 60 is linearly displaced bythe motor for purposes of applying a force to a valve stem 32 throughsurface contact with stem 32. This applied force causes a valve member34 to extend downward, disengaging valve member 34 from valve seat 36and thereby configuring valve 10 in an open position (e.g., as shown inFIG. 2). A compression spring 38 is preferably coupled to stem 32 tobias valve member 34 into engagement with valve seat 36.

Valve seat 36 and valve member 34 are located within a fluid conduit 18formed by base 12. Base 12 provides a platform for mounting valve stem32, spring 38 and bracket 14 of valve 10, in addition to its role inproviding a fluid path for engine exhaust. Specifically, base 12 forms afluid conduit 18 extending between a first port 20 and a second port 22.One of ports 20, 22 may be in fluid communication with an engine intakeor exhaust manifold. For example, port 22 may face an intake manifoldwhile port 20 faces a return exhaust passageway from the engine.

A valve portion 30 of valve 10 includes stem 32, spring 38, valve member34 and valve seat 36. Stem 32, having a first and second end 32 a and 32b, respectively, is connected to valve member 34 at end 32 b. End 32 ais preferably formed with a curved surface and includes a notchedportion 32 c for securing a cup 40 thereto. Cup 40 preferably takes theshape of a frustoconical-like element having a flange portion 40 a.Valve seat 36 and valve member 34 are made from a material suitablychosen to withstand high temperature loading conditions associated withan EGR environment.

Valve member 34 and valve seat 36 form a pintle-type valve. Other valvetypes may alternatively be used in place of a pintle-type valve, e.g., apoppet valve. Valve member 34 is upwardly tapered, and seat 36 iscorrespondingly shaped to receive valve member 34 to establish afluid-tight seal. When valve 10 is configured in an open position, valvemember 34 is disposed below seat 36, as can be understand by comparingFIG. 1 with FIG. 2. Valve stem 32 slides within a bearing element 44that is retained between a cup 42, gasket 14 a, base 12 and a pinprotector 47. At one end bearing 44 abuts a stem seal 46 and at theother end cup 42. Seal 46, which is preferably made from a hightemperature graphite, is included in valve 10 to prevent exhaust gasesfrom leaking past valve stem 32.

In a preferred embodiment, a spring, and more preferably, a linearspring 38 is used to bias valve member 34 into engagement with seat 36.Spring 38 is retained between annular flange 40 a and flange 42 a ofcups 40 and 42, respectively. The distance between flanges 42 a and 40a, and/or a spring stiffness is chosen so that a sufficient pre-load isapplied to retain valve 10 in a closed position using a pre-load inspring 38. Spring 38 is preferably a compression spring. As valve 10 isconfigured from a closed position to open position by applying adownward force on stem 32, spring 38 is compressed between flanges 40 aand 42 a.

In the embodiment of valve 10 illustrated in FIGS. 1 and 2, valveportion 30, which generally refers to spring 38, cups 40, 42, stem 32and valve member 34 may be decoupled from shaft 60 of actuator 16. Inother words, shaft 60 may be spaced from stem 32 (e.g., FIG. 2) so thatonly spring 38 influences the motion of valve member 34. This decoupledend 32 a is preferably formed with a curved surface and when abuttedwith actuator 16, this curved surface makes surface contact with apreferably flat face 61 of shaft 60.

Decoupled shaft 60 and stem 32 allows for assembly without having tomaintain a precise alignment between two or more components on anassembly line and will also tolerate slight misalignments between themotor and shaft 60. A disc-shaped body 60 c disposed at end 60 a ofshaft 60 can be included with shaft 60 so as to provide a relativelylarge contact area for stem 32 in the event of slight misalignmentsduring assembly. Decoupled shaft 60 also minimizes tolerance stack upproblems from the valve 10 components.

Decoupled shaft 60 and stem 32 will also facilitate a certain degree oftolerance for misalignments that may occur during valve operations. Forexample, if the line of action of shaft 60 “shifts” over time such thatthe force applied to stem 32 by shaft 60 is no longer co-linear with thelongitudinal axis of stem 32, shaft 60 may still be capable ofdisplacing valve member 34 from seat 36 without imposing undue stress onactuator 16 bearings. A misalignment, or “shift” between the line ofaction of shaft 60 and the stem 32 longitudinal axis may result from,e.g., repeated external mechanical vibrations that tend to loosenfittings between valve 10 components. Bearing 44, which guides stem 32,may be sized to allow a certain degree of “play” between stem 32 andbearing 44.

It is advantageous to minimize the amount of heat transfer from regionsof valve 10 in close proximity to exhaust gas to actuator 16 becausehigh actuator 16 temperatures can adversely effect the performance ofvalve 10. Accordingly, a preferred embodiment of an EGR valve, valve 10,includes an arrangement of components that attempts to minimize theamount of heat that is transferred from base 12 and/or stem 32 toactuator 16. Stem 32 and shaft 60, when they make contact, do so over arelatively small surface area. Additionally, bracket 14 is provided withopenings or cut-outs to allow air to come into contact with stem 32 andreduce the amount of heat transfer to actuator 16. An insulating coramicgasket 14 a, for example, is disposed between bracket 14 and base 12,which also reduces the amount of heat transfer from base 12 to bracket14. Cups 40 and 42 may also be configured to dissipate heat by formingflanges 40 a, 42 a as heat dissipating fins and cup 42 may be used as aheat isolator from bearing 44.

As mentioned earlier, actuator 16 includes a rotary motor and amechanism that is capable of displacing shaft 60 towards or away fromstem 32. Specifically, actuator 16 includes a mechanism that convertsrotary motion of the motor's rotor to linear motion in shaft 60. FIG. 3illustrate a preferred embodiment of this rotary to linear motiondevice. In this embodiment, shaft 60 includes a lead screw 62 having athreading 64 formed at end 60 b that is engaged with a threaded nut 66that is coupled in rotation to the motor's rotor. Lead screw 62 mayinclude a pair of flanges 68 that are received in stationary slots orchannels (not shown) within actuator casing 16 a to prevent rotation ofshaft 60 relative to nut 66. Thus, when a torque is applied to leadscrew 62 through nut 66, shaft 60 is linearly displaced as a result ofthe threaded engagement with nut 66. Any suitable rotary motor havingthe desired torque, speed and power characteristics may be used withvalve and its selection depends on the specific application.

In general, the factors that may be considered when selecting theappropriate actuator for valve operations include: ambient temperature(measured at the application site); self heat rise of the motor(measured at application site with embedded thermocouples); gross linearforce (e.g., poppet valve area×pressure+motor friction+pinfriction×1.5); diameter of the pintle; fail safe efficiency (e.g.,(Torque×2 PI)/(axial force×lead screw length)=fail safe efficiency) andreturn spring force (as discussed in greater detail below); and thedesired response to open and close the valve. Additionally, motorparameters (e.g., as provided by a motor supplier) such as resolutionper revolution (a function of the number of poles); detent torque; netforce deference between gross and needed or actual force; coefficient offriction of lead screw torque; and coefficient of friction of shaft sealtorque may be relevant to the motor selection for a particularapplication.

Actuator 10 includes a failsafe capability, as alluded to above. In oneembodiment, valve 10 includes a failsafe return spring, e.g., spring 38.In the event of a loss of power to the motor, spring 38 is designed toeffectively return the valve to the closed position, which in thepreferred embodiments requires that the spring be capable of backdrivingthe actuator. In this regard, the thread pitch should be suitably chosenso that it can be backdriven by the spring. Any of a variety ofactuators are believed to include a thread pitch that can meet therequirements for failsafe operations. Thus, the selection of a specificactuator will generally vary from application to application. Inselecting a spring for a failsafe operation, the following calculationmay be performed to determine whether the valve will remain closed(i.e., whether the spring pre-load is acceptable) when the valve issubjected to, e.g., a quasi-static 13 G load of the valve for thefollowing sample masses of component parts of a pintle-type valveembodiment: (Mass of Pintle Assembly + ½ Spring Mass + Mass of UpperSpring Cup)* Gload ≦ Spring Preload${\left( {\left( {{21.45\quad{grams}} + {0.5\quad\left( {6\quad{grams}} \right)} + {7.56\quad{grams}}} \right)*\frac{1\quad{kg}}{1000\quad{grams}}} \right)*\left( {13\quad G*\frac{9.81\quad m\text{/}s^{2}}{1\quad G}} \right)} \leq {25\quad N}$${4.09\frac{{kg}\quad m}{s^{2}}} = {{4.09\quad N} \leq {25\quad N}}$*Typical EGR Gload of 13 G was used for this calculation

In the illustrated embodiment, stem 32, valve member 34, cup 40, onehalf the mass of spring 38, and associated fasteners would represent themass in the above calculation.

While the present invention has been disclosed with reference to certainembodiments, numerous modifications, alterations and changes to thedescribed embodiments are possible without departing from the sphere andscope of the present invention, as defined in the appended claims.Accordingly, it is intended that the present invention not be limited tothe described embodiments, but that it has the full scope defined by thelanguage of the following claims, and equivalents thereof.

1. An exhaust gas recirculation valve, comprising: a base including afluid conduit extending between first and second ports; a valve memberdisposed within the fluid conduit, the valve member being configuredfrom a closed to an open position by linear displacement of the valvemember; a valve shaft having a first end fixed to the valve member; alinear actuator including a rotary motor, the linear actuator positionedto exert an actuator force on the valve shaft to displace the valveshaft in a first direction; and a valve spring disposed between theactuator and the valve shaft, the valve spring being positioned to exerta spring force on the valve shaft in a second direction opposite thefirst direction, the spring force being sufficient to back drive thelinear actuator.
 2. The-exhaust gas recirculation valve of claim 1,further comprising:. a pintle assembly including the valve shaft and amoving member of the valve member; and a spring cup connecting thespring with the valve shaft, wherein a preload on the spring is greaterthan a force represented by:(mass of pintle assembly+½ mass of valve spring+mass of springcup)*(expected acceleration load on exhaust gas recirculation valve). 3.The exhaust gas recirculation valve of claim 2, wherein the expectedacceleration load on the valve is 13 G.
 4. The exhaust gas recirculationvalve of claim 1, wherein the motor is a synchronous motor.
 5. Theexhaust gas recirculation valve of claim 1, wherein the actuatorincludes a member coupled to the motor's rotor and the member isdisposed adjacent to a second end of the valve shaft.
 6. The exhaust gasrecirculation valve of claim 5, wherein the member includes adisc-shaped end, the valve shaft includes a curved end, and wherein whenthe valve is configured in the open position, the curved surface is incontact with the member's end.
 7. The exhaust gas recirculation valve ofclaim 1, wherein the spring is a linear spring.
 8. The exhaust gasrecirculation valve of claim 7, wherein the valve shaft includes aflange and the spring is disposed between the flange and the valvemember.
 9. The exhaust gas recirculation valve of claim 8, the exhaustgas recirculation valve further including a bracket having a first endsecured to the base and a second end, wherein the actuator is disposedabove the bracket and the spring is disposed between the bracket firstand second ends.
 10. A method for failsafe operation of an exhaust gasrecirculation valve, comprising the steps of: providing a valve portionincluding a valve member engaged with a valve seat; providing a linearactuator for displacing the valve member, wherein the actuator ispowered by a rotary motor; providing a linear compression spring forexerting a spring force on the valve member; actuating the linearactuator to displace the valve member from a first position to a secondposition; and returning the valve member from the second position to thefirst position by back driving the rotary motor with the linearcompression spring.
 11. The method of claim 10, wherein the linearactuator has a thread pitch, and wherein the step of returning the valvemember from the second position to the first position by back drivingthe rotary motor with the linear compression spring further comprisesbackdriving the rotary motor through the thread pitch.
 12. The method ofclaim 10, wherein the second position corresponds to a closed valveposition.
 13. The method of claim 10, wherein the step of providing alinear actuator for displacing the valve member includes providing anactuator having an actuator shaft, the rotary motor displacing the shaftto first and second shaft positions corresponding respectively to theshaft being decoupled from the valve member and coupled to the valvemember.
 14. The method of claim 13, wherein the providing a linearactuator includes providing a disc-shaped element disposed at the end ofthe shaft.
 15. The method of claim 13, wherein the actuating stepincludes measuring a displacement of the shaft.
 16. The method of claim15, wherein the contacting step includes detecting an absence ofdisplacement of the shaft.
 17. The method of claim 16, wherein thedetecting an absence of displacement for a period of 100 milliseconds.18. The method of claim 13, wherein the actuator includes a sensor fordetermining the position of the shaft and the actuator includes arotation-to-displacement coupling between the shaft and the motor'srotor.
 19. The method of claim 13, wherein the motor has an axis ofrotation and the valve portion includes a stem having a longitudinalaxis that is substantially parallel to the axis of rotation, the stemhaving a first end that is fixed to the valve member and a second endadapted for being in contact with the shaft.
 20. The method of claim 13,wherein the shaft is decoupled from the spring.